III. Field
The present invention relates generally to communication, and more specifically to techniques for transmitting data in a multiple-input multiple-output (MIMO) communication system.
IV. Background
A MIMO system employs multiple (NT) transmit antennas at a transmitting entity and multiple (NR) receive antennas at a receiving entity for data transmission. A MIMO channel formed by the NT transmit antennas and NR receive antennas may be decomposed into NS spatial channels, where NS≦min {NT, NR}. The NS spatial channels may be used to transmit data in parallel to achieve higher throughput and/or redundantly to achieve greater reliability.
The MIMO channel between the transmitting entity and the receiving entity may experience various deleterious channel conditions such as, e.g., fading, multipath, and interference effects. In general, good performance may be achieved for data transmission via the MIMO channel if the interference and noise observed at the receiving entity are spatially “white”, which is flat or constant interference and noise power across spatial dimension. This may not be the case, however, if the interference is from interfering sources located in specific directions. If the interference is spatially “colored” (not white), then the receiving entity can ascertain the spatial characteristics of the interference and place beam nulls in the direction of the interfering sources. The receiving entity may also provide the transmitting entity with channel state information (CSI). The transmitting entity can then spatially process data in a manner to maximize signal-to-noise-and-interference ratio (SNR) at the receiving entity. Good performance can thus be achieved when the transmitting and receiving entities perform the appropriate transmit and receive spatial processing for the data transmission in the presence of spatially colored interference.
To perform spatial nulling of interference, the receiving entity typically needs to ascertain the characteristics of the interference. If the interference characteristics change over time, then the receiving entity would need to continually obtain up-to-date interference information in order to accurately place the beam nulls. The receiving entity may also need to continually send channel state information at a sufficient rate to allow the transmitting entity to perform the appropriate spatial processing. The need for accurate interference information and channel state information renders spatial nulling of interference not practical for most MIMO systems.
There is therefore a need in the art for techniques to transmit data in the presence of spatially colored interference and noise.